UBT Product Brochure - Evapco

SEISMIC FORCEThe Uniform Building Code categorizes geographicregions into one of four “Seismic Zones” based onthe probability and potential severity of a seismicevent. The zones are numbered 1 to 4 with Zone4 having the highest risk and strongest seismicforce potential.However, specifying mechanical equipment tomeet Seismic Zone 4 requirements is not enough.The forces that can be applied under Zone 4 varysubstantially. Many factors go into determining theactual force applied on cooling equipment. VolumeTwo of the 1994 Uniform Building Codeprovides the following formula to calculate theseismic force:This formula canexpress the force as apercentage of theequipment weight org’s. To calculate theLateral Force, Fp,the value of eachfactor must bedetermined. Thefactors are found inthe Uniform BuildingCode and vary basedon equipmentlocation and thetype of installation.Within Zone 4 it ispossible to calculatea horizontal accelerationranging from0.3g to 0.9g dependingon the method ofFp=ZIpCpWpFp = Lateral ForceZ = Zone FactorIp = Importance FactorCp = Horizontal Force FactorWp = Weight of EquipmentWithin Zone 4it is possibleto calculatea horizontalaccelerationranging from0.3g to 0.9gdepending on themethod ofinstallation and ...the mechanicalequipment’simportance.installation and the interpretation of the mechanicalequipment’s importance.Multi-directional seismic forces acting through center of gravityWith the development of the UB Series ® Products,EVAPCO has taken this subjective approach out ofdetermining the seismic requirement for mechanicalequipment. Based on actual forces experiencedduring recent earthquakes, EVAPCO designed theUB Series ® to withstand the following maximumaccelerations when applied concurrently to eachcomponent relative to the center of gravity:1.0g Horizontal0.3g Horizontal, Orthogonal0.5g VerticalThese seismic accelerations exceed themaximum requirement of Zone 4 and areindependently certified by Stone & WebsterEngineering Corporation. The accelerations includehorizontal concurrent with horizontal, orthogonaland vertical. The Uniform Building Code is limitedto horizontal force calculations. We have found thatmost seismic events include accelerationsin more than one direction and often includesubstantial vertical movement.In order to calculate the Lateral Force, Fp, the valueof the Zone Factor, Z, must be obtained. This variablerelates the risk and severity of force potential to eachgeographic region. A map of the United States in theUniform Building Code identifies each Seismic Zoneand applies a factor for each region.Seismic Zone 1 2A 2B 3 4Zone Factor 0.075 0.15 0.2 0.3 0.44